The present invention relates to a vehicle evaluation method and vehicle evaluation apparatus for a sense of lateral oscillation of a vehicle which is one evaluation criterion of riding comfort, and particularly to a vehicle evaluation method and vehicle evaluation apparatus for appropriately evaluating the sense of lateral oscillation of a vehicle based on muscular activity involved in maintaining the posture of the head of a passenger, and to a vehicle evaluation method and vehicle evaluation apparatus for appropriately and quantitatively evaluating the sense of lateral oscillation of a vehicle while turning based on the muscular activity involved in maintaining the posture of the head of a passenger.
Currently, various criteria are evaluated concerning the riding comfort of an automobile (vehicle). One such criterion of riding comfort is the sense of lateral oscillation. “Sense of lateral oscillation” means the positive or negative feel of the head oscillating in a lateral direction accompanying a rolling motion or lateral motion of the vehicle caused by disturbances in road surfaces and the like during linear travel. “A state of preferable sense of lateral oscillation” generally refers to cases where the sense of swaying is small.
The sense of lateral oscillation is generated because of irregular road surfaces and occurs even though the vehicle is in a state of linear travel, and is particularly noticeable in vehicles with high centers of gravity such as minivans and SUVs (sports utility vehicles).
However, the sense of lateral oscillation is difficult to predict due to the complex effects of vehicle characteristics such as roll rigidity, roll attenuation factor, center of gravity height, wheel rate, and the like.
Currently, the relationship between rates of vehicle acceleration and acceleration increase, and electromyograms of left and right sternocleidomastoid muscles, which contribute to stabilizing the head, is a subject of analysis (see Yoshiteru IWAMOTO, Daisuke UMEZU, Shigeru OZAKI, “Evaluating the Sensations of Automobile Drivers by Electromyogram”, 10th Conference of Japan Society of Kansei Engineering Preprint Collection, 2008; hereinafter referred to as Non-Patent Document 1). In Non-Patent Document 1, an approximation of the electromyograms of the sternocleidomastoid muscles is quantitatively calculated under the assumption that the electromyogram of the sternocleidomastoid muscles will be approximated by a linear sum of an acceleration rate (inertial force) and an acceleration increase rate.
Non-Patent Document 1 suggests that a change in the relationship between the acceleration rate and the acceleration increase rate in the forward and reverse directions of a vehicle and a calculated average waveform of activity of the left and right sternocleidomastoid muscles of the neck of the driver is possibly related to a sense of acceleration felt by the driver.
Furthermore, there are publications that focus on an amount of work being put upon the driver from an outside when turning a steering wheel due to irregular road surfaces and the like, and evaluate steering stability using a steering work rate which is a product of a steering force and a time derivative of a steering angle (i.e. steering speed) as an index (see JP 2002-214083A; hereinafter referred to as “Patent Document 1”).
Patent Document 1, for instance, describes an evaluation of vehicle steering stability based on data from a myoelectric sensor that detects the myoelectric potential of the triceps, flexor carpi ulnaris, extensor carpi ulnaris and other muscles of the arm.
The evaluation in Patent Document 1 uses a negative steering work ratio (a ratio of negative steering work to positive steering work), and evaluates steering stability to be high when the negative steering work ratio is small.
Furthermore, Patent Document 1 also describes a relationship between the myoelectric potential and the negative steering work ratio (refer to FIG. 9). In FIG. 9 of Patent Document 1, an upper right region is a region of poor linear stability, and a lower left region is a region of favorable linear stability. Accordingly, a relationship between an evaluation of the steering stability and the effects on the driver (what body parts are subjected to what forces) can be determined by the content of FIG. 9.